The present invention relates to a phase modulator and, more particularly, to a balanced type phase modulator for use in a microwave band.
A phase demodulator according to the prior art comprises, as illustrated in FIG. 4, a transformer 1 to which a local frequency or carrier frequency signal is inputted, a first Schottky barrier diode 13 connected to one terminal of the secondary coil (winding) of the transformer 1, a second Schottky barrier diode 14 connected to the other terminal of the secondary coil with the reverse polarity to the first Schottky barrier diode 13, and a capacitor 4 and a choke coil 5 connected in parallel to the connecting point between the first and second Schottky barrier diodes 13 and 14. In FIG. 4, a baseband signal is supplied through the coil 5, as a modulation signal.
In another phase modulator according to the prior art, as described in the Japanese Laid-open Patent Application No. 60(1985)-136455, the balance is adjusted by respectively applying bias voltages to two diodes.
However, the prior art phase modulator illustrated in FIG. 4 has a drawback of much signal loss, and, thus, has a problem that, for instance, the output level is low under predetermined intermodulation (IM).
On the other hand, in the phase modulator described in No. 60-136455, there is another problem of complex circuitry because it is necessary to supply the respective bias voltages to the two diodes.